Gas detector



Oct. 30, 1951 BLANCHARD 2,573,390

GAS DETECTOR Filed July 11, 1946 ff ii IN V EN TOR.

A DkE BLANCl-MRD BY W, W) fa ATTORNEYS released into the atmosphere.

Patented a. 30, 1951 GAS DETECTOR Andr Blanchard, Houston,".lex.,assignor to Schlumberger Well Surveying Corporation, Houston, Ten, acorporation of Delaware Application July 11, 1946, Serial No. 882,961

The present invention relates to apparatus for detecting the presence ofgas in a liquid. More specifically, it relates to a new and improvedapparatus for detecting the presence of gas in the drilling mud which iscustomarilyused to facilitate drilling operations in the oil industry.

It is the usual practice in drilling oil wells by the rotarymethod tocirculate a water or oil base drilling mud in the bore hole, whichserves both as a coolant and for bringing the drill cuttings to thesurface. When the drill penetrates into a gas bearing sand during thecourse of drilling operations, a quantity of the gas enters the drillingmud stream and is carried to the surface with the drill cuttings. Thepresence of this gas in the drilling mud isa detriment to properoperation since it tends to lighten the weight of the mud column andthus increase the danger of a blowout. For this reason, it is highlydesirable for the driller to know when the drill has reached a gasbearing formation, in order that he may take steps to increase thedensity of the drilling 2 Claims. (01. 13- 19) mud until the hydrostaticpressure of the mud I a gas bearing formation does not result in anyconsiderable continuous flow of gas into the drilling mud stream. On thecontrary, the amount of gas entering the mud stream is generally onlyslightly more than is present in the part of the formation removed bythe drill. This gas is carried to the'surface where it expands and isSince it is relatively-small in quantity and is given off only during arelatively short period of time, it is difflcult to detect. It isentirely possible, therefore, for the drill to traverse a gas zonewithout the q the drilling mud in an oil well, for example.

A'further object of the invention is, to provide va method and apparatusof the above character inwhich the properties of compressional waves areutilized for providing indications of the presence of gas in thedrilling mud.

' Another object of the invention is; to provide a novel gas detectingapparatus of the above character which is adapted to operateautomatically and unattended to provide a continuous record of gascontent versus time or drill depth, and/or to actuate a warning signalwhen the gas content in the drilling mud exceeds a safe amount.

In accordance with the invention, the presence of gas in the drillingmud of an oil well is detected by transmitting compressional wave energythrough the drilling mud stream at the surface and observing theattenuation of such wave energy produced by varying amounts of gascontained in the drilling mud. More specifically, the inventioncomprises the steps of producing wave energy, preferably but notnecessarily in the acoustic range, at a submerged point in the mudstream, and obtaining at another submerged point in the ,mud streamindications of the wave energy transmitted through the liquid betweenthe two points.

It has been determined that the eificiencyof propagation ofcompressional waves through a liquid is greatly influenced by thepresence of gas in the liquid. It has been found that the presence ofeven a small amount of gas in the liquid results in a marked reductionin the ability of the liquid to transmit wave energy. Other conditionsbeing fixed, the amount of absorption or attenuation of the acousticwave energy is related to the volume of the gas carried in the liquid.In general, the greater the percentage volume of the gas, the poorerwill be the transmission of acoustic waves by the liquid.

Since the acoustic wave transmission properties of the liquid depend onthe percentage volume of the gas contained therein, it will be apparentthat gas detectors relying on absorption or attenuation of wave energyfor their operation are not suitable for lowering in deep bore holes. Indeep oil wells, the ambient pressure is invariably very high so that thegreater portion of any gas present is in its liquid phase, and only asmall portion is in the gaseous phase. For this reason, it is proposed,according to the present invention, to detect the presence of gas in thedrilling mud at the surface or very near the point of exit of the mudstream, where the major portion of the gas in the mud stream is in thegaseous phase.

tion of a drill in a bore hole, showing the maninsure that a asvaaoc nerin which the drilling mud is circulated through the bore hole, and

Figure 2 is .a view in perspective of apparatus constructed according tothe invention for detecting the presence of gas in the drilling mud.

In Figure l, a conventional type drilling apparatus I is shown in a borehole ll. Drilling mud is pumped by suitable pumping apparatus (notshown) through the drill pipe I2 to the drilling head II where it flowsinto the bore hole In through the openings I4. tings from the bottom ofthe bore hole It are carried by the mud to the top of the bore holewhere they flow through a trough or conduit l5 into'a sump l6 from whichthe mud is recirculated through the bore hole It. Gas detectingapparatus D constructed according to the invention is submerged in themud in the trough I5 at the surface of the earth, so that the mud streamflows through it.

Referring now to the Figure 2, the gas de-a tecting apparatus Dcomprises an open-ended cylindrical conduit submerged in the mud streamflowing through the trough IS. A source of acoustical energy It such asa vibrating dia- The drill cut-- 2,451,797 and 578,531, now abandoned,filed Ibbe ruary 17,1946.

In operation, the conduit l1 andlassociated transmitter l8 and receiver2. are submerged in the mud stream in the trough ll (Figure 1) such thatat least a representative partof flow passes'continuously through theconduit 'l'l and the conduit I1 is maintained full'of fluid.

The ends'of the conduit I! may bejilared and quite readily.

The transmitter II is then energized at a constant frequency and powerlevel by the oscillator 19, thereby creating acoustical wave energythat'is propagated through the drilling mud to the receiver 2.. The moregas thereis present in the mud, the less will be the energy thatis=received at the receiver 2|. The output $01 the receiver 20, which isa function of the acoustical energy impinging upon it, is amplified, ifneephragm, for example, is positioned in oneside of the conduit II. Theacoustical energy source It may be energized by any suitable source suchas a fixed frequency oscillator Is, for example.

essary. by theampliner 2|. The output of the amplifier 2| may be changeto direct current.

by the rectifier 22 and may be recorded birecording meter :23. Theconcentration of gas present in the drilling mud may be re'adilydetermined by comparing the readingsof the meter-2l with a previouslyprepared calibration The oscillator l9 may'include any suitable numberof power amplifier stages as required to pro-,- duce a high enoughenergy level for proper op-, eration. A receiver 20, which may beanother microphone, is placed a short distance, from three inches to twofeet, for example, from the adjusted to operatefat the meter transmitterl8. The receiver 20 may be positioned within the conduit l1 orin anopposite wall thereof, as shown. Preferably the receiver 2|! ispositioned so that it will face thetransmitter It, in which case it willreceivemaximum energy therefrom.

Indications of the intensity of the acoustical energy received byreceiver 20 may be obtained in any conventional manner. One of manypossible indicating systems may comprise, for example. an amplifier 2|which receivesthe output of the receiver 20, the output of which may beindicated by a suitable alternating current meter. If desired, the.output of the amplifier 2| may be changed to a variable direct currentby a conventional detector or rectifier 22, the magnitude of the signalbeing indicated on presence of relatively'small quantities of a directcurrent meter 23. In a field unit, the a meter 23 will usually be, ofthe recording ,type. Any conventional alarm or warning means may beconnected in the output circuit such as in series or in parallel\vithvthe meter '23, and adjusted so that the alarm will sound whenthe-output is less than a predetermined value.

The conduit II should preferably be constructed of a material whichabsorbs sound the units It and 2|] should be suchas to peri mit theiroperation while submerged in the drilling mud. If microphonesorheadphone units are employed, they may be encased in a thin rubberjacket. Preferably, the acoustical generator should be of 'the typedisclosed in the co-pending patent applications of Andre Blanchard,Serial Nos. 578,529, now Patent No.

chartwhich gives meter readings versus different known mixtures ofdrilling mud and gas; If the danger point gas concentration has beendetermined, the alarm or warning device maybe reading corre sponding to:this critical value.

Itwill be apparent from the foregoingthat the invention provides ahighly satisfactory apparatus for detecting the presence of oil indrilling muds. By determining the absorption or attenuation ofcompressional wave energy propagated 4 through the; mud; stream nearthesurface of the earth,-in"accordance with the invention, the v I" ithe drilling mud, can be readily detected.

Other suitable devices for creating. the acoustic wave energy ofconstant, intensity, and other means for indicating the intensity of theacoustical energy received, will be readily apparent to those skilled inthe art, the specific apparatm' shown-being. onlyssehematic and typical.There,- fore, the novel apparatus disclosed herein'should', I beconsidered as illustrative of the invention and. scope of the appendedclaims. I

1. Apparatus for detecting the presence of gas in the circulatingdrilling mudqstream in an oil well comprising an open-ended conduit sub-..merged in said mud stream at the surface of not as limiting the Iclaim: 7

the earth and disposed so as to facilitate the flow of said mud streamtherethrough, a compressional wave energy transmitter mounted at oneside of said conduit, a constant intensity source of wave energy forsaid transmitter, a compressional wave energy receiver mounted at.another side of said conduit in the path of wave energy transmitted fromsaid transmitter through the mud stream, and means responsive to theoutput of said wave energyreceiver.

2. Apparatus for detecting the presence of gas a in the circulatingdrilling mud stream in an oil well comprising an open-endedconduitsubmerged in said mud stream at the surface of.

the earth and disposed so as to facilitate the flow of said mud streamtherethrough, a coinpressional wave energy transmitter mounted atrectifying means and providing a warning signal 4 when the output ofsaid wave energy receiver reaches a predetermined value.

ANDRE VBLANCHARD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED s'ra'rss mfrrm'rs' Number Name Date 1,570,781 Ruben Jan. 26, 19261,935,445 Heinz Nov. 14, 1933 2,214,674 Hayward Sept. 10, 1940 OTHERREFERENCES Book, Ultra Sonics, Bergman and Hatfield, John Wiley 8; Sons,N. Y., publishers, 1938 (pgs. 131, 132).

. Book, Supersonics, Robert Wood, published by Brown University,Providence, R. edition.

